1. Field of the Invention
The invention relates to the structure of a vertical axis wind turbine.
2. Description of the Related Art
As shown in FIG. 1, currently known a vertical axis wind turbine comprising a vertical axis wind mill 1 (the “wind mill”) and a generator 2 etc. The wind mill 1 consists of a plurality of blades 13 that attached to supporting arms 12, which are connected with vertical shaft 11. The generator 2 and the wind mill 1 are usually connected in either of the following methods:
One method, as shown in FIG. 2, is using a flange and bolts to connect the vertical shaft 11 to the top of the generator's rotor shaft 21. In such a structure, since the alternating load on the wind mill is assumed by the connecting parts of the vertical shaft 11 and the rotor shaft 12, the connecting part must be very strong. After certain period of operation, the wind mill may fall from the generator. Worse still, limited by the on-site assembly condition, the assembly precision is low, coupled by the fact that wind turbines are usually used in bad weather, the wind mill is prone to resonate under high wind conditions and resulting in damage thereto.
The other method, as shown in FIG. 3, is using a sleeve connection. The vertical shaft 11 is situated on a pedestal 6 under the base of the generator. In such structure, the load on the wind mill does not exert on the rotor shaft 21, and the rotor shaft 21 is exempted from axial and radial load. The vertical shaft 11 bears the wind mill's weight and the alternating load, conveying torque by a sleeve 3 around the rotor shaft 11 and a coupling 5. A bearing 43 and a bearing 44 (deep groove ball bearing, angular contact bearing, or roller bearing) are needed between the vertical shaft 11 and the sleeve 3 for supporting purpose. Therefore, vertical axis wind turbines adopting such structure are heavy in weight and complicated in structure, and breakdowns are common after long operation; furthermore, a pedestal is required, increasing both weight and cost. In on-site assembly of wind turbines of such structure, the generator is firstly fixed on the pedestal 6, with attention paid to maintain the concentricity of the pedestal and the generator. Then put the vertical shaft in the generator rotor's axis hole and attached to the pedestal. The tolerance for assembling the vertical shaft and the pedestal at the bottom of the generator is low to accommodate on-site assembly, resulting in instability occurred in rotation and shortened service life.
Besides, other parts, for example the supporting arms 12 and the vertical shaft 11, are assembled on-site. As shown in FIG. 4, holes are usually drilled in the flange 15 to connect the supporting arms by welding or bolting connection. Such assembly is inconvenient for larger wind turbines, and labor intensity is high.
As described above, parts of vertical axis wind turbines are usually delivered separately to installation site, and assembled and commissioned on-site. Therefore, on-site workload is increased. Limited by the on-site assembly condition, the stability and reliability of wind turbines are greatly undermined, resulting in shortened service life.
If the assembly is undertaken in the manufacturing facility, it is inconvenient to deliver. Further, because of the inherit defects with the above connecting methods, the stability, reliability, and service life of the wind turbines are greatly undermined.
Therefore, a new technology is anticipated to overcome the above problems.